A. Dornow and H. Machens described (Chem. Berichte 80, pp. 502-5 (1947)) the synthesis of 2,4,6-trimethyl-3-acetylpyridine by warming acetylacetone (2,4-pentane-dione) and ammonium acetate together on a waterbath. These authors suggest the following model for the reaction, in which one molecule of ammonia is condensed with one keto-form dione molecule and one enol-form dione molecule: ##STR1## Such a model is consistent with the fact that substantial dissociation of ammonium acetate into ammonia and acetic acid occurs at water (steam) bath temperatures.
A somewhat similar ammonia/diketone condensation reaction was reported (J. Het. Chem., 6, 771-3 (1969)) by E. Campaigne, D. McClure and J. Ashby. In this condensation, both molecules of the diketone apparently reacted in the mol form and the second stage of condensation required for ring closures did not take place: ##STR2## This reaction occurred when either ammonium acetate in acetic acid or gaseous ammonia in ethanol was employed.
Thus, it is surprising that the diazocine compound of the present invention, rather than the trimethyl-acetyl-pyridine, results when acetylacetone is reacted with free ammonia in methanol.
The present inventor has also found that the pyridine compound can be made by heating the subject diazocine in acetic acid. However, the mole ratio of unconverted diazocine to pyridine compound in the resulting reaction mixture is still about 1:3 after 1 hour at about 110.degree.-120.degree. C. Therefore, it is evident that the diazocine is not just a quasi-stable compound and cannot be assumed to have been involved as an intermediate in prior preparations of the pyridine.
A variety of substituted diazocine compounds are known. It is believed that the known compounds most closely related to the compound of the present invention, ##STR3## are as follows:
______________________________________ a. Monomers for preparation of polyamides. U.S.P. 3,503,939. ##STR4## b. Bacteriostats and fungistats. U.S.P. 3,236,837. ##STR5## c. Paudler & Zeiler, J. Org. Chem. 32, (8) 2425-30 (1967). Intermediates for preparation of compounds of undisclosed utility. ##STR6## ______________________________________